1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and more particularly, to a manufacturing method of a semiconductor device in which a predetermined pattern is formed in a film to be processed using a multilayer film.
2. Description of the Background Art
Recently, with the demands for miniaturization and high accuracy of a semiconductor device, it is a very important technical development issue to realize that a fine resist pattern is formed by lithography with high accuracy and a film to be processed is dry etched with high accuracy using the resist pattern as an etching mask at a fine processing step in its manufacturing process.
There are three restrictions mainly in forming the fine resist pattern by lithography as follows. Firstly, it is necessary to thin the resist as much as possible to improve resolution and prevent the pattern from being destroyed. Secondly, it is necessary to sacrifice plasma dry etching resistance in order to improve the resolution of a resist material. Thirdly, it is necessary to reduce a substrate reflection coefficient as much as possible in order to form the fine pattern with high accuracy.
Meanwhile, there are three restrictions mainly in dry etching the film to be processed using the resist pattern as the etching mask with high accuracy, as follows. Firstly, the etching mask has to have thickness to endure the dry etching for the film to be processed. Secondly, the etching mask has to have high selectivity for various kinds of film to be processed. Thirdly, the etching mask should not damage because of peeling after etching.
According to the conventional method using a monolayer resist on the film to be processed as the etching mask, it is hard to implement that the fine resist pattern is formed by lithography with high accuracy and the film to be processed is dry etched using the resist pattern as the etching mask with high accuracy. Thus, a process using a hard mask or a process using a multilayer resist has been developed for practical use.
Furthermore, a technique in which a photoresist is hardened by plasma containing bromide is disclosed in Japanese Patent Application Laid-open No. 2004-529231 or “Line edge roughness reduction by plasma curing photoresist.”, Proc. SPIE Vol. 5753, (2005) pp. 380-389, and a technique in which the etching resistance of the resist mask is enhanced by implanting Ar ion to the resist mask in which a pattern is formed by lithography is disclosed in Japanese Patent Application Laid-open No. 2001-358061, Japanese Patent Application Laid-open No. 2002-329648, and “Ar Ion Implantation into Resist for Etching Resistance Improvement”, Proc. SPIE Vol. 4345 (2001) pp. 655-664.
According to a general monolayer resist method, an organic or inorganic reflection preventing film to control reflection is formed on a film to be processed so as to have a film thickness of about 80 nm, and then a resist pattern having a film thickness of 250 nm to satisfy the dry etching resistance is formed thereon. When the pattern of 50 nm is formed, the aspect ratio=resist pattern thickness/resist pattern width is 5.0. In this case, since the aspect ratio of the resist pattern is too high, the pattern collapse is generated in the formed resist pattern.
When the film thickness of the resist is reduced to 120 nm to prevent the pattern collapse of the resist pattern, the resist cannot serve as the mask of the dry etching and the film to be processed after etching chips off. Thus, when the film thickness of the resist is reduced, the film to be processed chips off or its line edge is notched due to the resist deformation during the etching, so that the LER (Line Edge Roughness) of the film to be processed is increased.
When the film thickness of the resist is reduced to prevent the pattern collapse, and the hardening treatment to the resist is performed such that Ar, B, As, P, C, or H is implanted, reducing plasma such as H2, HBr or NH3 is used, DUV (Deep Ultraviolet) or VUV (Vacuum Ultraviolet) is light-irradiated, or EB (Electron Beam) is irradiated in order to enhance the dry etching resistance, the pattern deformation (e.g., leaning or excessively shrinkage in a large pattern) is generated depending on the layout of the resist pattern, so that the problem is that the pattern size is different from that originally designed. In the case where Ar, B, As, P, C or H is implanted into the resist, this pattern deformation is caused by the structure change in the resist film by a reducing effect generated by the implantation energy. In other hardening treatments, similar pattern deformation is generated although its degree is different, which is a big problem in manufacturing the device. That is, according to the above method, although the chipping off or LER of the film to be processed after etching can be improved, fidelity to the original design considerably deteriorates.
According to a multilayer resist method, a lower organic film is applied to a film to be processed as a lower-layer hard mask (HM), a SOG film (silsesquioxane film) having high etching selectivity is thinly applied to the lower organic film as a middle layer, and a conventional monolayer resist pattern is formed thereon. According to the multilayer resist method, the middle layer and the lower-layer HM are dry etched sequentially and finally the film to be processed is etched using the lower-layer HM pattern as an etching mask. In this multilayer resist method, when the selectivity between the lower organic film having high dry etch resistance and the middle layer used for etching it is ensured and the reflection coefficient can be controlled at the lithography step, the restrictions described in the background art can be all cleared. However, even in the multilayer resist method, although both lower layer and middle layer are required to be more rigid as the pattern becomes fine, sufficiently uniform rigidity is not always provided in the coating type film by the heat hardening treatment only and as a result, the LER deterioration is generated in the pattern after etching.
Furthermore, there is a multilayer hard mask (HM) method in which an amorphous carbon (α-C) layer is formed on a film to be processed by CVD, a silicon nitride film or a silicon oxide film having high etching selectivity for the (α-C) layer is formed by CVD as a middle layer and the conventional monolayer resist pattern is formed thinly thereon. According to this multilayer hard mask method, the middle layer and the (α-C) layer are sequentially dry etched and finally the film to be processed is etched using the pattern of the (α-C) layer as an etching mask. According to this multilayer hard mask method, since a uniform and rigid film can be formed as compared with the coating type multilayer resist method, it clears all the restrictions described in the background art. However, the problem in the multilayer hard mask method is that reflection coefficient control and chemical compatibility with the resist are bad.
In addition, when the multilayer hard mask method is applied to the via-first dual damascene step, although it is necessary to bury a lower-layer amorphous carbon (α-C layer) into a via hole, there is a problem in filling characteristics of the amorphous carbon. In addition, although it is necessary to remove the buried amorphous silicon after the trench etching, since the amorphous carbon is rigid, it is difficult to remove it and as a result, the Low-k interlayer insulation film deteriorates (rise in k value).